linux-kernel - Re: [PATCH v2] selftests/resctrl: fix clang build warnings related to abs(), labs() calls

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Date: Tue, 7 May 2024 15:30:51 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: John Hubbard <jhubbard@...dia.com>, Shuah Khan <shuah@...nel.org>
CC: Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers
	<ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, Justin Stitt
	<justinstitt@...gle.com>, Fenghua Yu <fenghua.yu@...el.com>, Valentin Obst
	<kernel@...entinobst.de>, <linux-kselftest@...r.kernel.org>, LKML
	<linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>
Subject: Re: [PATCH v2] selftests/resctrl: fix clang build warnings related to
 abs(), labs() calls

Hi John,

On 5/3/2024 4:40 PM, John Hubbard wrote:
> First of all, in order to build with clang at all, one must first apply
> Valentin Obst's build fix for LLVM [1]. Furthermore, for this particular
> resctrl directory, my pending fix [2] must also be applied. Once those
> fixes are in place, then when building with clang, via:
> 
>     make LLVM=1 -C tools/testing/selftests
> 
> ...two types of warnings occur:
> 
>     warning: absolute value function 'abs' given an argument of type
>     'long' but has parameter of type 'int' which may cause truncation of
>     value
> 
>     warning: taking the absolute value of unsigned type 'unsigned long'
>     has no effect
> 
> Fix these by:
> 
> a) using labs() in place of abs(), when long integers are involved, and
> 
> b) Change to use signed integer data types, in places where subtraction
>    is used (and could end up with negative values).
> 
> [1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/
> [2] https://lore.kernel.org/all/20240503021712.78601-1-jhubbard@nvidia.com/
> 
> Cc: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
> 
> Hi Reinette,
> 
> This v2 includes a fix for the bugs that you pointed out (thanks!) in v1.
> 
> I kept the changes to signed integers minimal: only what is required in
> order to get a clean clang build.
> 
> thanks,
> John Hubbard
> 
>  tools/testing/selftests/resctrl/cmt_test.c | 12 ++++++------
>  tools/testing/selftests/resctrl/mba_test.c |  4 ++--
>  tools/testing/selftests/resctrl/mbm_test.c |  4 ++--
>  3 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cmt_test.c b/tools/testing/selftests/resctrl/cmt_test.c
> index a81f91222a89..af33abd1cca7 100644
> --- a/tools/testing/selftests/resctrl/cmt_test.c
> +++ b/tools/testing/selftests/resctrl/cmt_test.c
> @@ -29,22 +29,22 @@ static int cmt_setup(const struct resctrl_test *test,
>  	return 0;
>  }
>  
> -static int show_results_info(unsigned long sum_llc_val, int no_of_bits,
> -			     unsigned long cache_span, unsigned long max_diff,
> -			     unsigned long max_diff_percent, unsigned long num_of_runs,
> +static int show_results_info(long sum_llc_val, int no_of_bits,
> +			     long cache_span, long max_diff,
> +			     long max_diff_percent, long num_of_runs,
>  			     bool platform)
>  {
> -	unsigned long avg_llc_val = 0;
> +	long avg_llc_val = 0;
>  	float diff_percent;
>  	long avg_diff = 0;
>  	int ret;
>  
>  	avg_llc_val = sum_llc_val / num_of_runs;
> -	avg_diff = (long)abs(cache_span - avg_llc_val);
> +	avg_diff = labs(cache_span - avg_llc_val);
>  	diff_percent = ((float)cache_span - avg_llc_val) / cache_span * 100;
>  
>  	ret = platform && abs((int)diff_percent) > max_diff_percent &&
> -	      abs(avg_diff) > max_diff;
> +	      labs(avg_diff) > max_diff;
>  
>  	ksft_print_msg("%s Check cache miss rate within %lu%%\n",
>  		       ret ? "Fail:" : "Pass:", max_diff_percent);

The changes in this hunk are unexpected. The changes to this area made by previous
version was ok, no? It really seems like this just does a brute force of everything
to long (while taking labs() twice) unnecessarily.

> diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c
> index 7946e32e85c8..707b07687249 100644
> --- a/tools/testing/selftests/resctrl/mba_test.c
> +++ b/tools/testing/selftests/resctrl/mba_test.c
> @@ -60,8 +60,8 @@ static bool show_mba_info(unsigned long *bw_imc, unsigned long *bw_resc)
>  	/* Memory bandwidth from 100% down to 10% */
>  	for (allocation = 0; allocation < ALLOCATION_MAX / ALLOCATION_STEP;
>  	     allocation++) {
> -		unsigned long avg_bw_imc, avg_bw_resc;
> -		unsigned long sum_bw_imc = 0, sum_bw_resc = 0;
> +		long avg_bw_imc, avg_bw_resc;
> +		long sum_bw_imc = 0, sum_bw_resc = 0;
>  		int avg_diff_per;
>  		float avg_diff;
>  

On second look it only seems necessary to change avg_bw_imc and avg_bw_resc. What do you think?


> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
> index d67ffa3ec63a..30af15020731 100644
> --- a/tools/testing/selftests/resctrl/mbm_test.c
> +++ b/tools/testing/selftests/resctrl/mbm_test.c
> @@ -17,8 +17,8 @@
>  static int
>  show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span)
>  {
> -	unsigned long avg_bw_imc = 0, avg_bw_resc = 0;
> -	unsigned long sum_bw_imc = 0, sum_bw_resc = 0;
> +	long avg_bw_imc = 0, avg_bw_resc = 0;
> +	long sum_bw_imc = 0, sum_bw_resc = 0;
>  	int runs, ret, avg_diff_per;
>  	float avg_diff = 0;
>

Same here wrt the avg_ variables.

  
> 
> base-commit: ddb4c3f25b7b95df3d6932db0b379d768a6ebdf7
> prerequisite-patch-id: b901ece2a5b78503e2fb5480f20e304d36a0ea27
> prerequisite-patch-id: 8d96c4b8c3ed6d9ea2588ef7f594ae0f9f83c279

Reinette